Belt cleaning systems for conveyors that utilize a scraper blade to remove debris and other materials from conveyor belts are well known. These conveyor belts often include metallic splices extending across the belt that run past the scraper blades during conveyor belt operations. The scraper blades are typically biased into engagement with the belt to allow them to scrape leavings off of the belt and yet resiliently shift away from the belt when surface irregularities on the belt are encountered such as due to the aforementioned metallic splices.
Generally, the goal of keeping the scraper blade in substantially constant contact with the belt to improve cleaning thereof is in competition with the need to allow the blades to shift away from the belt to avoid taking the full brunt of impacts with metallic splices and the like which can cause the scraper blades to rapidly wear. In heavier duty applications, this problem can be exacerbated by the use of thicker, more robust fasteners which create higher impact loads on the cleaning blade.
Cleaners that have an arcuate or “U” shape are known in the art, such as disclosed in U.S. Pat. No. 5,978,281. Such cleaners are adapted to operate on the underside of a conveyor belt to scrape carry-back or leftover materials that remain stuck to the belt after transfer of the bulk material. The arcuate shape of the blade helps maintain contact between the blade and the belt to maximize cleaning efficiency near the center of the belt, where most of the cleaning is required.
The blade of the '281 patent is comprised of a plurality of metal plates having scraping portions held together with a resilient member, which connects the supporting members and allows the band to be formed into the shape of the blade holder which is carried rearwardly in the downstream return travel direction of the belt. The resilient member has a lower leg portion that may be inserted into a holding groove of the blade holder. An extended standing portion projects from the holding groove and contacts the belt and includes a downstream head portion formed by a gradual thickening of the extended standing portion in the downward and rearward directions so that the upper portion of the resilient member including the standing portion and head portion thereof has a generally wedge-shaped configuration. Notably, a jaw is formed at the downstream side of the head portion, so that there is a lower, transverse shoulder surface extending between the scraper head and specifically the jaw portion thereof, and the narrow, lower leg portion with the shoulder surface which contacts and covers over the downstream or rear side wall of the holder. This jaw is described as preventing biased abrasion of the scraping portion by supporting the extended standing portion against the moment produced toward the return travel direction of the belt during operation. Biased abrasion, or abrasion of the belt by the scraper tip at an angle other than perpendicular, is not preferred, because it is less effective for cleaning the belt.
However, due to tolerances in the manufacturing process of the blade, the blade holder, and other factors in the installation and operation of a scraper in accordance with the '281 patent, the jaw often may not operate effectively to prevent biased abrasion. Specifically, the overhanging jaw portion must be in contact with the top surface of the downstream side wall of the holder in order to support the extended standing portion against the moment produced by abrasion of the belt. Small discrepancies in the location of the jaw portion on the blade, the height of the downstream side wall, or the length of the leg portion may cause a gap to be present between the jaw portion and the downstream side wall of the holder. In addition, residue of scraped-off material may become deposited in the holder over time, causing the entire blade to sit higher in the holder, thus lifting the jaw portion out of contact with the holder wall.
In addition, the blade disclosed in the '281 patent has a rubber sheet that is bonded to the blade with the rubber sheet including a skirt portion that extends over a wall of the blade holder. The rubber sheet guides material that has been scraped from the belt along the sheet and toward the outer side of the holding wall of the holder to prevent the material from becoming lodged in the holding groove of the blade holder. Over time, the rubber sheet tends to wear down and may fall off once the bond between the rubber sheet and the blade is broken. Once the rubber sheet comes loose from the blade, scraped material may bond in and around the area between the scraper blade and the blade holder, making it extremely difficult to remove the scraper blade from the holder when the blade is ready for replacement.
The process of adhering the rubber sheet has certain disadvantages, such as the increased time, labor, and materials. The rubber sheet is made prior to the manufacture of the main body of the blade, including the molding of the resilient member to the metal support members. To affix the rubber sheet to the blade, an adhesive layer is applied to the upstream side of the metal support members and the upper portion of the rubber sheet is applied to the adhesive layer. The metal support members and rubber sheet are then disposed in a die and rubber is introduced into the die to form the resilient member and capture the support members therein.
Another issue with prior art blades is that the blade tips may fracture due to stresses imposed during the manufacturing process. In particular, a carbide blade tip may be fixed to the tip of a rigid steel plate using a brazing process. As the rigid plate is subject to heat, thermal expansion occurs in the plate, and as the plate cools after the carbide tip has been brazed to the plate, the plate contracts and may subject the tip to large stress concentrations. As the carbide tip is brittle in comparison with steel, the tip may crack due to the stresses caused by the contraction of the plate. Such cracking increases cost and manufacturing time and can cause the blade to perform poorly.